Perfect was the captivity of Gwair in Caer Sidi, Thanks to Pwyll and Pryderi’s emissary
Before him no one entered in to it, The heavy, dark chain held the faithful youth
And before the spoils of Annwfn sorely he sang, And thenceforth remains he till doom a bard
Three freights of Prydwen went we thither, But only seven returned from Caer Sidi
In Culhwch and Olwen, Arthur’s band of men set sail to Ireland aboard his ship Prydwen to acquire the cauldron of Diwrnach. However, Diwrnach treats them to a feast but denies them the cauldron. One of Arthur’s warriors, LLenlleawc the Irishman, kills Diwrnach’s entire retinue using Caledfwlch (Caliburn or Excalibur).
Geoffrey of Monmouth states in his 12th century Historia regum Britanniae that Pridwen is Arthur’s shield. However, this conflicts with his shield having earlier been named as Wynebgwrthucher in Culhwch and Olwen, and also the fact that both previous works - i.e. Culhwch and Olwen and Preiddeu Annwfn, have declared Prydwen to be Arthur’s ship.